1. Field of the Invention
This invention relates to a roller contact device suitable for use in a tap changer or the like, and more particularly to an improved roller contact device in which a plural number of pairs of roller contacts are bridged to contact (bridge-contact) with a pair of stationary contacts, so-called a bridge-type roller contact is used.
2. Description of the Prior Art
It is known in a conventional roller contact device using a bridge-type roller contact that an electric current path from a stationary contact, i.e. a first stationary contact to the other stationary contact, i.e. a second stationary contact flows in the following order:
a first stationary contact; PA1 a point of contact of the first stationary contact with a roller contact; PA1 the roller contact; PA1 a point of contact of the roller contact with the second stationary contact; PA1 the second stationary contact. The current path is made by interposing only the roller contact between the two stationary contacts. In other words, since there no interpositions in the current path except for the roller contact (e.g., a roller shaft for rotatably supporting the roller contact, or slidably contacting portions including bearings fitted between the roller contact and the roller shaft), it has the excellent features that electrolytic corrosion does not occur at the slidably contacting portions, and the roller contact can always be maintained in a smooth rotating status.
Now, in a case where an increased current capacity is required for such a roller contact device, it has been suggested that a plural number of roller contacts are arranged in parallel.
Referring to FIG. 8, there is shown an example of the conventional roller contact device of this type in which two roller contacts 5F and 5B are disposed before and behind a first and second stationary contacts 6U and 6L.
In the drawing, the two roller contacts are inserted in parallel in a current path from the first stationary contact to the second stationary contact. Therefore, a current capacity will be redoubled compared with a case where one roller contact is inserted in the current path. Further, it is also suggested in this conventional device that when the current capacity is required to be further increased, two more roller contacts may be disposed in parallel to have a total of four roller contacts and as a result, the current capacity will be further redoubled.
By the way, in case that the four roller contacts (two each) are disposed in parallel before and behind the stationary contacts, a question arises as to how to support them. In the conventional roller contact device, there is only suggested a concrete supporting structure in which two roller contacts are separately arranged. Further, in case the two roller contacts are increased by plural times, there is only suggested a supporting structure in which the structure for supporting the two roller contacts is simply increased by plural times. However, as seen in the conventional suggestions, if the supporting structure for the two roller contacts is simply increased by two times, the device has problems or drawbacks that it requires multiple number of component parts and it is not only uneconomical, but also the overall size must be bulky.